Radio frequency (RF) transceivers and receivers can be found in numerous applications, particularly in the field of wireless communications and radar sensors. In the automotive sector, there is an increasing demand for radar sensors used in so-called “adaptive cruise control” (ACC) or “radar cruise control” (RCC) systems. Such systems may be used, for example, to automatically adjust the speed of an automobile so as to maintain a safe distance from other automobiles or other objects ahead.
Modern radar systems make use of highly integrated RF circuits, which may incorporate all core functions of an RF front-end of a radar transceiver in one single package (single chip transceiver). Such RF front-ends may include, inter alia, a voltage controlled oscillator (VCO), amplifiers such as power amplifiers and low noise amplifiers (LNAs), mixers, and directional couplers. Furthermore, the single chip transceiver may include circuit components for analog base band signal processing and an analog-to-digital converter (ADC) for subsequent digital signal processing. As mentioned, the RF frond-end as well as the base band signal processing may be integrated in a single chip also referred to as monolithic microwave integrated circuit (MMIC).
Radar applications used in automobiles are subject to various standards concerning road traffic safety, for example the functional safety standard ISO 26262 entitled “Road vehicles—Functional safety”. To ensure the functional safety of a radar sensor, it is important to know whether the current state of the radar sensor allows a e.g., reliable distance and speed measurement. However, also in applications different from radar, reliability may be an issue. With regard to reliability of the radar measurements, one issue is impedance matching, e.g., establishing matched impedances of the output port of the RF front-end and the antenna. Any defect in the RF transmission line between the MMIC and the antenna may deteriorate the impedance matching and cause reflections. Furthermore, any object close to the antenna which obstructs radiation from the antenna, may deteriorate the impedance matching.